the idea:
there's one big file (diary)
its size is set on creation and constant
its filled with random data
the file begins with a long which is total length of the diary, encrypt
inside it there are entries:
- timestamp
- start index of previous entry (encrypted of course)
- length of data
- data
you can't edit data if there's a newer entry
each entry is encrypted

there's also an index file:
- total length of diary
-